Liquid chromatographic determination of vitamin K1 in infant formulas and milk

Vitamin K1 in infant formulas and milk products is determined by reversed-phase liquid chromatography (LC) with UV detection. The sample is hydrolyzed enzymatically, and the vitamin is extracted with hexane. Fractionation by normal-phase semi-preparative LC is followed by analytical LC, with quantitation by the internal standard technique. Recovery of the analyte was 97.4 +/- 2.8%. Linearity was established between 0.05 and 4.0 micrograms/mL. The limit of quantitation is 0.5 microgram/100 g for milk powder, which allows the method to quantitate endogenous levels of vitamin K1.